The region has already been plagued by a similar tragedy in March 31 - May 14 2007, when a total of 928 seals, including 710 baby seals, died near the Kalamkas oil field.
A research group from Kazakstan's Biological Security Research Institute and Institute of Microbiology and Virology cited the phocine distemper virus (PDV), which has been blamed for the deaths of fin-footed mammals all over the world since 1988, as responsible for the deaths.
Though samples revealed that both PDV or increased levels of heavy metals were present in the carcasses, some experts believe that environmental pollution suppressed the seals' immune system and made them vulnerable to the disease.
Poor weather has also made its contribution, as ice cover in the Caspian Sea did not appear until late February, and melted completely by March 20. Such conditions could have had a negative effect on baby seals.
In 2000, chronic intoxication killed 10,500 seals in the region. For several years the animals had been absorbing oil toxins and pesticides, which damaged their immune resistance, the experts said.
